Formability Assessment of C1100 Pure-Copper Tube Considering an Enhanced Modified Maximum Force Criterion

The Modified Maximum Force Criterion (MMFC) and Marciniak-Kuczynski (MK) models were initially developed to evaluate strain localization in sheet metals. This study investigates their use in predicting the forming limit diagram (FLD) of a tubular material, specifically C1100 pure-copper tubes. To achieve this, uniaxial tensile tests were performed to develop a robust constitutive model, capturing the material's hardening behavior with a combined Swift-Voce hardening law. A MATLAB code was then developed to theoretically predict the FLD using an enhanced MMFC model, termed MMFC2, alongside the established MK model. These predictions were validated against experimental results from tube expansion tests. Additionally, the theoretical FLDs were integrated into finite element simulations of the tube expansion test to forecast tube bursting behavior. The comparisons reveal that the MMFC2 model's predictions align more closely with experimental outcomes than those of the MK model, highlighting MMFC2's superior potential for predicting FLDs in tubular materials.